Each element \(\mathbf {B}_{h}\in \mathbf {V}_{h}^{\operatorname{face}}(K)\)  is uniquely determined by its
normal components on the elemental faces, i.e., the set of constant
values of \(B_{F}=\big (\mathbf {B}_{h}\cdot \mathbf {n}_{F}\big )_{F\in \mathcal {F}^{K}_{h}}\) .
We take these values as the degrees of freedom of \(\mathbf {B}_{h}\)  and refer the
reader to [1]} for the
proof of their unisolvence.
A major consequence of such a space definition is that \(\Pi ^{0,K}_{0}\mathbf {B}_{h}\) 
and the divergence of \(\mathbf {B}_{h}\)  are computable from the degrees of
freedom of \(\mathbf {B}_{h}\)  for all \(\mathbf {B}_{h}\in \mathbf {V}_{h}^{\operatorname{face}}(K)\) .
